Issue for this PR

Closes #17765

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

On Windows Desktop, all session history disappears every time the client is closed and reopened. The sessions still exist in the SQLite database but the UI shows an empty list.

Root cause: Path normalization was inconsistent across different parts of the system:

• project.worktree stored as "/" (Unix-style root)
• session.directory stored as "C:\" (Windows path format)
• lastProjectSession key stored as "/"

This path mismatch prevented the Desktop UI from matching/loading existing sessions after restart.

Solution: Added consistent path normalization in two places:

1. packages/app/src/utils/path-key.ts - Simplified pathKey() to properly handle Windows root paths (e.g., C:\ or /) -> normalize to /
2. packages/opencode/src/session/session.ts - Added normalizeDirectory() helper to normalize directory paths before storing sessions

How did you verify your code works?

1. Manually edited the Desktop's opencode.global.dat file to fix path mismatches (changing "/" to "C:\" for worktree and lastProject)
2. Confirmed sessions reappeared in the sidebar after the path fix
3. The fix ensures new sessions are created with normalized paths, preventing future mismatches

Screenshots / recordings

N/A - This is a backend fix, not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR